Introduction/Methods. The proposed study will address a very important issue for the VA both currently and in the future -- the high percentage of OIF/OEF/OND Veterans who have been medically diagnosed with a mild traumatic brain injury (mild TBI) and experience distressing symptoms. Smart phone mobile applications have become a primary source of information and communication among large percentages of Americans, especially those of the OIF/OEF/OND generation. The proposed study is a 4-year randomized control trial investigating the utility of an interactive, self-management smartphone application, TBI Coach, one of a suite of mobile applications developed by VA. The primary goal of the proposed study is to evaluate the efficacy of TBI Coach for improving clinical outcomes in those with a history of mild TBI and to determine what aspects of TBI Coach are most useful to Veterans. An overarching goal of this line of research is to improve access among Veterans with mild TBI who still have symptoms months to years after injury. Objectives. The study will pursue the following objectives: (1) Evaluate the efficacy of TBI coach for improving clinical outcomes among recipients of TBI Coach. (2) Determine the aspects of TBI Coach most associated with positive outcomes. (3) Obtain qualitative information on factors associated with use of TBI coach or with deriving benefit from use of TBI Coach that can be used to inform future modifications of the application and wide scale implementation. Potential Impact. This study will be the first to systematically evaluate one of VA's smart phone applications, both through RCT and qualitative interview, thereby gaining a summative evaluation of TBI Coach. The information obtained will inform strategies to improve the application and spread its use to Veterans who may be able to benefit from it. It will also provide information that may inform rollout of other smart phone applications.